There is an increasing demand within the cable television (CATV) industry for a subscriber control device which resides outside of the subscriber's residence and which is fully controlled by the cable operator at the headend. Such a device would eliminate the need for individual set top subscriber units which translate all selected programming onto a single VHF channel and would therefore allow the subscriber to obtain full use of sophisticated features now available on television receivers and VCRs.
Such control devices allow all programming channels available to a cable subscriber to be selected by the subscriber's receiver or VCR, but these devices also incorporate means to selectively interdict or "jam" certain signals on those channels on a per subscriber basis in order to provide for pay television or subscription television services.
Existing devices include control systems in which multiple fixed oscillators are coupled to multiple subscribers through a switching matrix. The control capacity of such systems is limited however, because each oscillator interdicts a single signal. Systems have also been proposed which use one or more oscillators which are frequency agile and which can jump from one frequency to another under programmed control, in order to interdict more than one signal. Such systems however utilize a jamming unit containing oscillator and the associated control circuitry, for each subscriber. This is expensive in terms of physical size, power required and cost of materials.
One object of the invention therefore, is to provide a subscriber control device which provides substantial control of the program signals available to a cable subscriber but at reduced cost and increased efficiency and flexibility of service.